The thermodynamics for the quantum three wave interaction model is studied in the Fermion Case I. It is found that the Bethe Ansatz method by Yang and Yang is applicable to this model. The integral equations for the thermal equilibrium and excited states are derived.
The classical version of the three-wave interaction models the creation and destruction of waves; the quantized version models the creation and destruction of particles. The quantum three-wave interaction is described and the Bethe ansatz for the eigenfunctions is given in closed form. The Bethe equations are derived in a rigorous fashion and are shown to have a thermodynamic limit. The Dirac sea of negative energy states is obtained as the infinite density limit. Finite particle/hole excitations are determined and the asymptotic relation of energy and momentum is obtained. The Yang–Yang functional for the relative free energy of finite density excitations is constructed and is shown to be convex and bounded below. The equations of thermal equilibrium are obtained.
Abstract The Thermodynamic Bethe Ansatz (TBA) allows us to study finite size and finite temperature effects of an integrable model. This chapter investigates the integral equations that determine the free energy and gives their physical interpretation. It discusses Casimir energy, Bethe relativistic wave function, the derivation of thermodynamics, the meaning of pseudo-energy (dressed energy and momentum), infrared and ultraviolet limits, the coefficient of bulk energy, the general form of the TBA equations, the thermodynamics of the free field theories, L-channel quantization and the LeClair–Mussardo formula. It also covers the application of the Yang–Lee S-matrix, the magnetic field Ising model, and the tricritical Ising model.
Abstract The thermodynamics of a quantum field theory in an infinite volume can be determined by its S-matrix. This idea, originally proposed by R. Dashen, S.K. Ma, and H.J. Berstein, has been widely used to study the thermal properties of the integrable field theories in (1 + 1) dimensions. The reason consists of the particularly simple properties of these scattering matrices, as discussed in the previous two chapters, and the possibility to generalize to the relativistic case the thermodynamics Bethe ansatz (TBA) techniques successfully applied to non-relativistic problems by C.N. Yang and C.P. Yang. In the TBA approach, the derivation of the thermodynamics of a purely elastic scattering theory reduces to finding the solution of a set of nonlinear integral equations that rule the energies of the particle excitations and their statistical distribution.